The production of the cytokines, interferon-gamma and tumour necrosis factor by human antral mucosa cells and stimulated peripheral blood mononuclear cells were determined by enzyme linked immunosorbant assay and L929 bioassay respectively. Tumour necrosis factor production by peripheral blood mononuclear cells in response toHelicobacter pylori stimulation was depressed inHelicobacter pylori positive individuals, compared toHelicobacter pylori negative individuals (P < 0.05). There was no difference in tumour necrosis factor production by peripheral blood mononuclear cells in response to purified protein derivative. However, tumour necrosis factor production by cells isolated from gastric mucosa during short term culture was significantly higher inHelicobacter pylori positive patients (P < 0.05) than negative patients, indicating a probable macrophage response. Levels of interferon-gamma did not differ significantly in the gastric explant culture from the two groups. The results show thatHelicobacter pylori negative patients have a stronger peripheral cellular immune response toHelicobacter pylori infection. The higher levels of tumour necrosis factor production by antral mucosa cells inHelicobacter pylori positive patients may reflect the infiltration of T lymphocytes and macrophages within the local mucosa.